It is currently causing a trap, but the reason is not clear:

nsncd[1179]: unhandled signal 7 code 0x1 at 0x00ffffff8184e920 in libc.so.6[ffffff81824000+1aa000]
CPU: 3 PID: 1179 Comm: nsncd Not tainted 6.1.72 #1-NixOS
Hardware name: riscv-virtio,qemu (DT)
epc : 00ffffff8184e920 ra : 00ffffff8184e868 sp : 00ffffffef6ab610
 gp : 00aaaaaac0f07db8 tp : 00ffffff81822780 t0 : 00ffffffef6ab1f0
 t1 : 00aaaaaac0e5283c t2 : 0000000000000b56 s0 : 00ffffffef6ab668
 s1 : 0000000000000001 a0 : 0000000000000001 a1 : 00ffffffef6ab668
 a2 : 00ffffffef6ab678 a3 : 00aaaaaac0f06e40 a4 : 0000000100000000
 a5 : 00aaaaaac0eac296 a6 : 00ffffff819d3048 a7 : 00ffffffef6ab8c0
 s2 : 0000000000000000 s3 : 00aaaaaac0efac40 s4 : 00aaaaaac0e6755a
 s5 : 00ffffffef6ab678 s6 : 00aaaaaac0efac48 s7 : 00ffffff81a2fd58
 s8 : 00ffffff81a30030 s9 : 00ffffffd7386ef0 s10: 0000000000000000
 s11: 0000000000000000 t3 : 00ffffff8184e818 t4 : 0000000000000028
 t5 : 00ffffff81a24380 t6 : 00ffffff81a074c8
status: 0000000200004020 badaddr: 00aaaaaac0eac296 cause: 0000000000000000

In order to build the kernel without compressed instructions we need to
disable EFI support. We also need to leave the kernel to figure the
proper -march and -mabi flags, as otherwise it fails to build. Using the
option "CONFIG_RISCV_ISA_C n" disables the use of compressed
instructions.

Prevents mass rebuilds in x86, where the envvar doesn't have any effect.

In QEMU the kernel is loaded at the ${kernel_addr_r} address and we need
to use booti instead of bootm.

Booting the kernel works, but by manually specifying the address.

Add VisionFive 2